Re: Small correction in http://www.postgresql.org/docs/9.0/interactive/wal-reliability.html

On 06/17/2011 07:55 AM, Achilleas Mantzios wrote:
> It reads :
> 'On FreeBSD, IDE drives can be queried using atacontrol, and SCSI drives using sdparm.'
> but it should be:
> 'On FreeBSD, IDE drives can be queried using atacontrol, and SCSI drives using camcontrol.'
>

FreeBSD's Common Access Method (CAM) looks to be the preferred driver
layer to interrogate.  sdparm is available on Linux and FreeBSD, but
it's a second-class citizen talking to CAM on the latter.  To quote from
one of the docs on it, FreeBSD sdparm "SCSI commands are routed through
the CAM pass-through interface".  Talking directly to it with camcontrol
does seem to be the preferred route for some things.

However, the UI to sdparm is a bit easier to use when it is available.
Actually changing the write cache state with camcontrol requires black
magic--you have to construct the right SCSI packet by hand.  I can't
find any example.

Bruce just touched this section of the docs recently, so this part
actually reads just:

          SCSI drives use <command>sdparm</command>.

Now.  Perhaps the following makes sense:

          SCSI drives can be queried using <command> camcontrol
identify</command>, and the write cache both queried and changed using
<command>sdparm</command> when available.

--
Greg Smith   2ndQuadrant US    greg@2ndQuadrant.com   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support  www.2ndQuadrant.us